Chemokine receptors cell-surface expression

Receptor desensitization is commonly caused by receptor internalization, whereby the receptor is removed from its location on the membrane into the cytoplasm, and then either degraded or recycled back to the surface by two main mechanisms. The level of cell-surface expression of a chemokine receptor is a balance between the rate of internalization and the rate of recovery, which can occur via de novo receptor production or receptor recycling, and which in some cases is a constitutive process (Pelchen-Matthews et al., 1999). Internalization is dramatically increased in the presence of agonist, and it is an active process, as internalization is almost entirely prevented at temperatures below 16°C (von Zastrow and Kobilka, 1994). There appear to be two main mechanisms of chemokine receptor internalization 1) the classical recruitment of arrestin to the receptor, resulting in the formation of a clathrin-coated vesicle around the receptor and subsequent internalization, and 2) internalization via clathrin-independent pathways. 

Fig. 1. Surface phenotype of HSPCs. Primitive HSPCs have the phenotype of c-KitThy-ll0WLin CD34+CD33 in humans, and the mouse counterparts have the phenotype of c-KifThy-llowLin Sca-l+. Primitive HSPCs express CXCR4 as the major chemokine receptor and various adhesion molecules such as VLA-4, VLA-5, LFA-1, P-selectin glycoprotein ligand-1 (PSGL-1), and CD44 for migration to the stem cell niche.

Shimaoka T, Nakayama T, Fukumoto N, et al. Cell surface-anchored SR-PSOX/ CXC chemokine ligand 16 mediates firm adhesion of CXC chemokine receptor 6-expressing cells. J Leukoc Biol 2004 75(2) 267-274. 

Macrophage presence and reactivity in tissue sites are elicited though different combinations of effector molecules (e.g., cytokines, chemokines) acting on specific receptors thus, the expression and presence of given membrane receptors on macrophage cell surfaces correlate to specific (acquired) functions and activation profiles.18 Furthermore, macrophage maturity and/or differentiation state is/are often characterized based on the presence or absence of specific surface receptors (e.g., F4/80 +, Mac-1 + Figure 2.1).61 Receptor profiles vary between cells of different maturity, primary and secondary derivation, and between cell lines.62... 

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